Mugil cephalus fish is from euryhaline fish, so its gills have the ability for accommodation in both
fresh and marine water. We studied the histological changes in gill epithelium at the age of three, six,
eight months and one year as well as, expression of PPARα, PPARγ, BCL-2, BAX, KI67, and PCNA
in gills epithelium. We used hematoxylin and eosin staining for general histological observations. As
well as, we detected Immunofluorescence of PPARα, PPARγ, BCL-2, BAX, KI67, and PCNA
antibodies. General histological observations detected that the gill filament was supported by hyaline
cartilage and some connective tissue fibers, from the gill filament several secondary lamellae
projects. There were several kinds of cells present in gill filament and secondary lamella e;
mitochondria-rich cells (MRCS), pavement cells, mucous cells, red blood cells, pillar cells, melanincontaining macrophage and undifferentiated cells at the apex of gill filament. The mitochondria-rich cells gave a positive reaction with PPARγ which indicated a role of PPARγ in osmoregulation process performed by MRCS. However, PPARα was highly positive in red blood cells which suggested its role in respiration process. In all examined ages there was a high number of proliferative and apoptotic cells widely distributed all over the gills. An essential role of PPARγ in the process of osmoregulation was observed and an important role of PPARα in the respiratory function of gills. As well as, we distinguished the ability of gills epithelial cells to proliferate under the control of PCNA and KI67 for the maintenance of normal gill structure in hazard conditions. Also damaged cells undergo apoptosis process under the control of BAX and the anti-apoptotic process performed in gills under the control of BCL2 gene.